A Sirocco Warden Captain commands a patrol and wears the bronze shoulder-clasp that says so. Captains are Lyceum graduates who took the field rather than a clerkship, and they hold their posting by competence rather than birth: a captain who loses people at the dome's edge answers for it to the High Magisters in person.
They are the rank the city actually meets. A captain decides whose weapons are taken at a gate, whose caravan is searched, and which body pulled out of the deep desert is worth the water it would take to revive. Captain Tariq al-Senna is one of them.